Tooth forms for roller chain sprockets, referred to as ISO tooth forms, are defined in ISO 606: 1994 (E). FIG. 17 shows an ISO tooth form, and FIG. 18 illustrates the engagement between a roller chain and a sprocket having the ISO tooth form shown in FIG. 17.
In the ISO tooth form shown in FIG. 17, when the chain pitch is p, the pitch circle diameter is d, the roller outer diameter is d1, the radius of the arc of the tooth gap bottom portion is ri, the tooth surface radius is re, the diameter of the tooth gap bottom is df, and the number of sprocket teeth is z, the relationships of these parameters are defined by the following expressions from ISO 606: 1994 (E):d=p/sin(180°/z)df=d−d1re(max)=0.12 d1(z+2)ri(min)=0.505 d1re(min)=0.008 d1(z2+180)ri(max)=0.505 d1+0.069 (d1)1/3
As apparent from the above expressions, in the ISO tooth form shown in FIG. 17, the tooth gap bottom portion 3 is in the form of an arc having a radius ri, which is slightly larger than the radius (d1/2) of the roller 62, and the tooth surface 2 is in the form of an arc having a radius re. The tooth surfaces 2 are continuous with on both sides of the tooth gap bottom portion 3. Further, as apparent from the above expressions, the diameter df of the tooth gap bottom is equal to the difference between the pitch circle diameter d and the roller outer diameter d1. Furthermore in view of the above expressions, the diameter df of the tooth gap bottom is substantially the same as the difference between the pitch circle diameter d and twice the arc radius ri of the tooth gap bottom portion.
As shown in FIG. 18, when a chain 61 is in mesh with, and partly wrapped around, the sprocket 1 having the ISO tooth form, and the chain and sprocket are in use for power transmission, a roller 62 meshes with the sprocket 1 at a tooth gap bottom portion 3, and polygonal motion of the roller chain 61 occurs, as is well known. This polygonal motion allows the roller chain 61 to pulse. The pulsing in turn vibrates the roller chain 61, which causes generation of noise. Furthermore, this polygonal motion generates a speed change in the roller chain in the advancing direction.
A system to decrease the pulse motion of the roller chain due to polygonal motion has been devised, in which the sprocket comprises sprocket teeth, each having a front tooth surface (relative to the direction of rotation), a rear tooth surface, and an asymmetric tooth groove for receiving a roller, formed of a front tooth surface and a rear tooth surface of an adjacent tooth. The asymmetric tooth groove has a flat portion formed on a front tooth surface. This system is described in Japanese Patent No. 2002-514287
However, the roller chain sprocket of Japanese Patent No. 2002-514287 leaves room for further improvement in the reduction of pulse motion of the roller chain due to polygonal motion.
Accordingly, an object of this invention is to provide a sprocket for a roller chain or bushing chain, in which the amount of pulse of the chain due to the polygonal motion is further reduced and the roller or bushing more smoothly disengages from the sprocket.